Epstein-Barr virus (EBV) of man and herpesvirus papio (HVP) of baboons are related and are representative of B-lymphotropic viruses. Herpesvirus saimiri (HVS) of squirrel monkeys and Herpesvirus ateles (HVA) of spider monkeys, also related, are representative of T-lymphotropic viruses. All four viruses induce lymphoproliferative diseases in marmoset monkeys (Saquinus and Callithrix sp.) and transform in vitro human or nonhuman primate lymphocytes into continuous growing lymphoblastoid cell lines. The genomic relatedness of EBV and HVP will be further determined by analyses of viral DNA by heteroduplex tests and restriction enzyme cleavage patterns. Selected marmoset species will be studied for susceptibility to infection with well-defined strains of EBV. Studies with HVS will focus on comparing an attenuated strain of HVS (A-HVS) with oncogenic HVS (O-HVS) with respect to course of experimentally-induced infection in marmosets. A-HVS, in contrast to O-HVS, does not induce a fatal lymphoproliferative disease but instead a life-long latent infection. Emphasized in the EBV and HVS studies in vivo, will be evaluation of humoral and cell-mediated immune responses to viral-specified and lymphocyte detected membrane antigens and characterization of the neoplastic cells for chromosomal abnormalities and biochemical surface membrane properties which may be associated with malignant transformation but absent in lymphocytes transformed in vitro. Presently no definitive marker exists for differentiating A-HVS and O-HVS, therefore extensive comparative studies will be performed in vitro for defining a distinct difference between the two viruses; molecular biology techniques will be employed for comparative analyses of viral DNA. The transforming potential in vitro of HVA for marmoset lymphocytes has been well established and we will concentrate on determining the optimal conditions for transformation of marmoset and human lymphocytes and demonstrate lymphocyte transforming activity of viral DNA.